1. Field of the Invention
The present invention relates to an encoder used together with an electric motor.
2. Description of the Related Art
An encoder is used for detecting an angular position of a rotary body which is directly or indirectly driven by an electric motor. To prevent the entry of foreign matter, the component parts of the encoder are held inside a housing unit provided with a sealing member (see Japanese Utility Model Registration No. 3188676). If an electric motor is used for driving a spindle or travel axis of a machine tool, the encoder will be exposed to a cutting fluid or washing solution. The housing unit holding the component parts of the encoder has a liquid-tight structure protecting these component parts from the cutting fluid etc. In particular, at a boundary part of the housing and cover forming the housing unit, an O-ring or other sealing member is provided.
However, if a cutting fluid or washing solution with a strong attack property deposits and remains in the gap between the housing and the cover, the housing or cover is liable to gradually corrode and the liquid-tightness is liable to be impaired.